The present invention relates to the assembly of drive mechanisms for engines, more particularly a yoke mechanism. More particularly, it relates to improvements in the ease of assembly of both the components of a wobble yoke mechanism and of the wobble yoke mechanism itself into the engine.
The wobble yoke mechanism can be used in conjunction with internal or external combustion engines, compressors, refrigeration equipment, hydraulic pumps and the like. Preferably the present invention relates to a wobble yoke used with external combustion engines, and more preferably with Stirling engines.
Methods known to the applicant for fitting a drive mechanism, and specifically a yoke mechanism, to an engine do not lend themselves well to simple and efficient assembly. As will be understood, the use of a yoke mechanism (or drive mechanism, generally) in such an application, for converting the reciprocating motion of a piston of the engine to rotation of a crankshaft or vice versa, requires a mechanical connection between the piston and the yoke mechanism.
Typically such a connection in a conventional engine is performed with a connecting rod of a known type. Both ends of such rods are pivotally connected, one to the piston (by a gudgeon pin assembly) and the other to the yoke mechanism. Each piston and connecting rod, with associated components, are inserted into the respective cylinder. The yoke mechanism is then assembled piecewise onto the engine block and fixed to the connecting rods.
In applications such as Stirling engines, however, where connecting rod seals are present, the piston may only be inserted from one end of the cylinder, thus further limiting the options for providing a modular assembly which can be readily mounted to the engine.
It is equally desirable that these components can be quickly and easily disassembled from the engine block, for maintenance and repairs on the engine or wobble yoke assembly. Fitting the yoke mechanism in the manner described above is time consuming, it also requires technically precise workmanship, and this is a drawback which also increases manufacturing cost, since more costly skilled labor is required.
A similar problem exists in servicing the engine in the field, as anyone who needs to work on the engine and disassemble it, needs to do this delicate work on site. This can lead to difficulty, as often a repair and maintenance workman is not sufficiently skilled for this work. Further, in performing any repairs it is desirable to reduce to a minimum the time taken, as down time can be costly and disruptive. This is particularly true when the site of the engine is remote.
It is an object of the present invention to provide a yoke engine mount which overcomes these difficulties and which allows for ready assembly of the yoke mechanism and engine parts to the engine.
Another object of the invention is the provision of a yoke engine assembly that can be easily removed and replaced as a single unit, so that the engine may continue to operate with a replacement assembly while the malfunctioning assembly can be taken away for repair.
A further object of the invention is to improve the facility with which the components of the yoke mechanism itself may be assembled.
It is a still further object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.
According to one aspect of the present invention there is provided a mounting assembly for connection of a drive mechanism to an engine wherein the said drive mechanism connects one or more pistons of an engine and an output shaft, the engine having an engine block, the drive mechanism being selected from the group: a wobble plate, a wobble yoke of a type described in WO 94/27064, and another wobble yoke mechanism; and wherein the drive mechanism includes a connecting rod for connection to each piston of the engine; said assembly including:
pedestal, to which the drive mechanism is mounted such that a torque reaction of the output shaft passes through the said pedestal, the pedestal being fixed to an output Shaft side of the engine block by releasable fastening means accessible only from the said output shaft side of the engine block; and whereby,
each connecting rod includes means for releasable connection of said rod to a corresponding piston of the engine,
characterized in that the connection of each rod to the respective piston is effected with the piston positioned within the respective cylinder of the engine.
According to another aspect of the present invention there is provided a mounting assembly for connection of a drive mechanism to an engine, as described above, wherein the pedestal includes:
a flange at one end adapted for mounting the pedestal to the engine block, said flange including a pattern of spaced apart holes, for receiving the fastening means therethrough, and a first part of a two part locating mean so said pattern matching a corresponding pattern of holes in the engine block; whereby
a second part of the said two part locating means on the engine block, in conjunction with the said fasteners and flange, locates the said pedestal with respect to the engine block.
Preferably, the fastening means are screws and the holes in the engine block are screw threaded. Preferably the spanner used for the screws is a prismatic type, such as an Allen key.
According to another aspect of the present invention there is provided a mounting assembly for connection of a drive mechanism to an engine, as described above, wherein the drive mechanism includes openings therethrough adapted for the insertion of fastening means and tools.
According to another aspect of the present invention there is provided a mounting assembly for connection of a drive mechanism to an engine, as described above, wherein the mounting assembly further including a screw threaded section on each connecting rod for fixing the connecting rod to a corresponding threaded part of the piston.
According to another aspect of the present invention there is provided a mounting assembly for connection of a drive mechanism to the block of an engine, as described above, wherein said connecting rods are pivotally connected to a beam of the drive mechanism assembly, and wherein the centre of said pivotal connection describes a path having a small component perpendicular to a sliding axis of the piston; and wherein
each said of connecting rods includes a profiled section having a lower bending stiffness in at least one plan than any adjacent sections of the rod.
This provides a flexure joint to assist in the assembly of the attached pistons into the said engine wherein this flexure joint also reduces the side thrust imposed on the piston by the connecting rod, due to the small component of the motion of said centre perpendicular to the sliding axis of the piston.
According to yet another aspect of the present invention there is provided an improved means of constructing a drive mechanism, as described above, wherein said drive mechanism is a wobble yoke of a type described in WO 94/27064, and the said pivotal connection between the pedestal and a first and a second beam is made between a known universal cross component and the said beam or beams, said cross being fastened by known means to the said pedestal.
Preferably, the said beams and yokes are manufactured using a casting process. Preferably, bearings connecting the first beam and a first yoke and the second beam and a second yoke include axial and radial load capacity. Preferably, said bearings are taper roller bearings. Preferably, a bearing fitted to or about the shaft of the engine is insensible to alignment errors. Preferably, the said bearing is a spherical roller bearing.
According to another aspect of the present invention there is provided a method of assembly for an engine, said method including the steps of:
(a) providing the engine, engine block, pistons and mounting assembly as described above;
(b) securing the components of the drive mechanism to the pedestal, and securing each connecting rod to the drive mechanism, thereby forming a sub-assembly;
(d) mounting the sub-assembly to the engine block, said mounting including guiding the second end of each connecting rod into the respective engine cylinder, and locating together the two part locating means;
(e) releasably securing the sub-assembly to the engine block with the fastening means; and
(f) releasably securing each piston to the second end of the respective connecting rod.
According to a still further aspect of the present invention there is provided a method of assembly, as described above, wherein the drive mechanism is of a type described in WO 94/27064, having two beams and two lower drive mechanisms, wherein the method further includes before step (b), the step:
securing the lower yokes to the beams and the beams to a universal cross, which forms a component of the drive mechanism for mounting the drive mechanism to the pedestal.
According to another aspect of the present invention there is provided a method of replacement of a drive mechanism, rod and mounting assembly for an engine, said method including the steps of:
(a) providing an engine assembled by the above described method;
(b) unscrewing each of the pistons from the respective connecting rod;
(c) de-mounting the sub-assembly;
(d) replacing the sub-assembly; and
(e) re-assembling the engine using the method of assembly described above.